1. Field of the Invention
The present invention relates to a process for manufacturing tyres for vehicle wheels.
The invention also relates to an apparatus for the deposition of at least one reinforcing element on a toroidal support, said apparatus being able to be used to carry out the aforementioned process.
2. Description of the Related Art
In the present description and in the subsequent claims, the term “reinforcing element” is used to indicate an element comprising one or more thread-like reinforcing elements, such as textile or metallic cords, incorporated in, or coated with, a layer of elastomeric material.
It should also be specified that, in the present description and in the subsequent claims, the term: elastomeric material, is used to indicate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such a composition also comprises additives like, for example, a cross-linking agent and/or a plasticiser. Thanks to the provision of the cross-linking agent, such a material can be cross-linked through heating, so as to form the final product.
A tyre for vehicle wheels generally comprises a carcass structure comprising at least one carcass ply formed from reinforcing cords incorporated in an elastomeric matrix. The carcass ply has end edges respectively engaged with annular anchoring structures, arranged in the areas usually identified with the name “beads” and normally each formed from a substantially circumferential annular insert on which at least one filling insert is applied, in a radially outer position thereof. Such annular structures are commonly referred to as “bead cores” and have the task of keeping the tyre well fixed to the anchoring seat specifically provided in the rim of the wheel, thus avoiding in operation the radially inner end edge of the tyre coming out from such a seat.
At the beads specific reinforcing structures can be provided having the function of improving the torque transmission to the tyre. The region of the beads, indeed, is particularly active in the transmission of torque from the rim to the tyre when accelerating and when braking and, therefore, the provision of appropriate reinforcing structures in such an area ensures that the torque transmission occurs with the maximum possible reactivity.
In a radially outer position with respect to the carcass ply a belt structure comprising one or more belt layers is associated, said belt layers being arranged radially one on top of the other and having textile or metallic reinforcement cords with crossed orientation and/or with an orientation substantially parallel to the direction of circumferential extension of the tyre.
Between the carcass structure and the belt structure a layer of elastomeric material can be provided, known as “under-belt”, having the function of making the radially outer surface of the carcass structure as uniform as possible for the subsequent application of the belt structure.
In a radially outer position with respect to the belt structure a tread band is applied, also made from elastomeric material like other structural elements making up the tyre.
Between the tread band and the belt structure a so-called “under-layer” of elastomeric material can be arranged, said layer having properties suitable to ensure a steady union of the tread band itself.
On the side surfaces of the carcass structure, respective sidewalls of elastomeric material are also applied, each extending from one of the side edges of the tread band up to the respective annular anchoring structure to the beads.
Conventional manufacturing processes of tyres for vehicle wheels essentially provide for the components of the tyre listed above to be firstly made separately from each other, to then be assembled in a subsequent building step of the tyre.
Nevertheless the current tendency is that of using manufacturing processes that allow the production and storage of semi-finished products to be minimised, or possibly, eliminated.
More specifically, attention has now turned towards process solutions that allow the individual components of the tyre to be made by directly applying them, according to a predetermined sequence, onto the tyre being built on a forming support, typically toroidal or cylindrical.
For example, in document WO 01/36185 to the same Applicant, the components of the tyre are made on a toroidal support by sequentially depositing a plurality of reinforcing elements thereon, the reinforcing elements consisting for example of individual rubberised cords or of rubberised cords grouped in parallel in the form of strip-like elements, particularly used in making the carcass and belt structure, and of continuous elongated elements in elastomeric material, particularly used for making the other structural components of the tyre, such as for example tread band, sidewalls, liners, fillers.
Document U.S. Pat. No. 6,355,126 describes for example a method and an apparatus for making a belt layer through deposition on a suitably positioned forming support of band-like pieces cut from a continuous band-like element. The band-like pieces, once cut from the continuous band-like element, are picked up through gripping means and moved to the forming support for deposition.
In EP 1 418 043 A2 a method and an apparatus for forming an annular elastomeric component of a tyre, in particular an insert for filling the beads, are described. The described method comprises an annular extrusion step of elastomeric material on a forming support and a modelling step, through the action of a modelling extruder on the surface of the forming support, of the material deposited to obtain the desired profile for the component.
In U.S. Pat. No. 6,379,493 B1 a device for the transportation and deposition onto a forming support of a tyre of pieces cut to size of elastomeric material is described, said pieces being in particular intended to form inserts for filling the beads. The device comprises rotatable gripping devices which are movable along a direction essentially tangential to the circumferential surface of the forming drum and which allow each piece to be gripped and deposited in a predetermined position on the forming drum.
With particular reference to the region of the tyre defined at the bead, the Applicant has realised the importance of providing in this region a reinforcing structure, as described with reference to the tyre structure discussed above.
In conventional processes, the reinforcing structure intended to be applied in the region of the bead of the tyre consists of one or more semi-finished products made in the form of reinforced continuous band-like elements. Such band-like elements are made separately from the rest of the components of the tyre and then assembled on the tyre in the building step of the tyre. These band-like elements, in particular, are associated with the tyre in the building step in a side-by-side relationship.
The Applicant has considered the problem of making and applying, on a substantially toroidal forming support, a reinforcing structure comprising one or more reinforcing layers, each of which comprising a plurality of reinforcing elements orientated in a non-circumferential direction, for example in a substantially radial direction, in the region of the bead of the tyre in a process for producing tyres for example of the type described in document WO 01/36185 mentioned previously.
The Applicant has verified the possibility of forming on a substantially toroidal forming support a reinforcing structure as described above by applying at least one reinforcing element along a predetermined curvilinear deposition path, said deposition path being defined for example at the region of the bead on a not perfectly planar surface of the forming support.